1. Weather

2. Making Weather Forecasts  Weather Measurements are Made  Measurements are Put Into Weather Forecast Models  The Models are Interpreted

3. Weather Instruments  Thermometers – measure air temperature  Barometer – measures air pressure  Psychrometer – measures relative humidity, using the cooling effect of evaporation  Anemometer – measures wind speed

4. More Instruments  Weather Balloons – measure weather conditions higher in the atmosphere  Weather Map – shows all the data that meteorologists collect, using symbols  Weather Satellites – photograph and track large scale air movements  Computers – used to compile and analyze data

5. Main Factors that Influence Weather  The Sun – amount of sunlight determines climate –Amount of solar energy affects precipitation and evaporation  The Water Cycle  The Atmosphere – protects Earth from extreme temperatures and conditions

6. The Building Blocks of Weather  Includes clouds, precipitation, and wind  Type and intensity of weather is controlled by changes in air pressure –Air pressure is caused by the weight of the air molecules above –High pressure causes air to flow down and fan out –Low pressure causes the air to rise and cool, forming clouds

7. Air Masses and Fronts  Air Mass – large region above the Earth with a fairly uniform temperature and moisture level  Storms usually form when a cold, dry air mass interacts with a warm, moist air mass  The point where the two masses meet is called a front.

8. Fronts  Warm Front– warm air is moving toward cold air –Shown as red line with scallops  Cold Front – cold air is moving toward warm air –Shown as a blue line with arrow points  Stationary Front – if neither mass is moving very much –Shown as an alternating red and blue line

9. Other Terms Affecting Weather  Continental Deflection – surface currents change direction when they meet continents  Coriolis Effect – the curving of surface currents due to the Earth’s rotation  Trade Winds – the persistent flow of the near-surface winds over tropical oceans

10. Thunderstorms  Form when an air mass becomes unstable and overturns violently –Air in the lower layers is unusually warm and humid, or the upper layers are unusually cool  Lightning – electricity that forms in the strong up- and-down air currents in a storm cloud  Thunder – lighting heats the air around it causing it to expand rapidly, which sends out vibrations we hear as sound

11. Tornadoes  A violently rotating column of air that descends from a thunderstorm  Forms when three very different types of air come together and there is a change in wind speed and direction with height  Tornado winds can reach 300 miles per hour

12. Hurricanes  Swirling storm measuring 60 – 1,000 miles in diameter that forms over warm ocean waters (MUST BE WARM !)  Begins as a cluster of strong thunderstorms moving across an ocean called a tropical wave –Progresses to a tropical depression, then a tropical storm, and once the winds reach 74 mph or greater, it becomes a hurricane

13. More About Hurricanes  Typhoon- hurricane that forms in the Pacific  Cyclone – forms in the Indian ocean  Parts of a Hurricane: –Eye : center where it is quiet and clear –Eye Wall : strongest part of the hurricane –Rain Bands : spiraling bands of clouds where rains and winds decrease as they move away from the eye

14. El Nino  A warm current in the Pacific Ocean off the coast of South America  Causes unusual weather patterns all over the world  Occurs every 2 to 7 years  Sometimes followed by La Nina, a cold ocean current